The present invention relates to a capacitance element using a capacitance insulating film made of a dielectric material with a high dielectric constant or of a ferroelectric material and to a manufacturing method therefor.
As higher-speed and lower-power microcomputers have been implemented in recent years, electronic devices to be used as consumer products have remarkably increased in performance, while semiconductor elements composing a semiconductor device used therein have been rapidly scaled down. Under such circumstances, undesired radiation which is electromagnetic noise generated from the electronic devices has presented a serious problem. As a measure to suppress the undesired radiation, attention has been focused on the technique of embedding, in a semiconductor integrated circuit or the like, a capacitance element with large capacitance using a capacitance insulating film made of a dielectric material with a high dielectric constant (hereinafter simply referred to as a high-dielectric-constant material). As higher integration has been achieved in a dynamic RAM, on the other hand, extensive research has been conducted on the technique of using a high-dielectric-constant film as a replacement for a silicon oxide film or silicon nitride film that has been used previously. Additionally, vigorous research and development has been directed toward a ferroelectric film having the property of spontaneous polarization to implement an industrially usable non-volatile RAM capable of operating at low voltage and performing high-speed writing and reading operations.
To implement a semiconductor device having the performance described above, it is important to devise a capacitance element having such a structure as to allow higher integration without degrading the properties of the capacitance element and a manufacturing method therefor.
Referring to the drawings, a conventional capacitance element and a manufacturing method therefor will be described. FIG. 9 is a cross-sectional view of a principal portion of the conventional capacitance element, in which are shown: a substrate such as a silicon substrate with an integrated circuit formed therein; a lower electrode 22 of the capacitance element which is composed of a platinum film or the like; a capacitance insulating film 23 of the capacitance element which is composed of a thin ferroelectric film; and an upper electrode 24 of the capacitance element which is composed of a platinum film or the like. The upper and lower electrode 24 and 22 and the capacitance insulating film 23 constitute the capacitance element. There are also shown: an aperture 25 formed in the capacitance insulating film 24; an interlayer insulating film 26 covering the capacitance element; a first contact hole 27 extending through the interlayer insulating film 26 to reach the lower electrode 22; a second contact hole 28 extending through the interlayer insulating film 26 to reach the upper electrode 24; a first electrode wire 29 to be connected to the lower electrode 22; and a second electrode wire 30 to be connected to the upper electrode 24.
The recent trend has been to compose each of the electrode wires 29 and 30 of a multilayer film such as a two-layer film consisting of an upper-layer aluminum-alloy film containing aluminum as a main component and a lower-layer titanium film or a three-layer film consisting of an upper-layer aluminum-alloy film containing aluminum as a main component, an interlayer titanium nitride film, and a lower-layer titanium film. In the case of embedding such a capacitance element in an integrated circuit, in particular, the first and second electrode wires 29 and 30 are also connected directly to a diffusion region in the integrated circuit, so that the titanium film is normally used to compose the lowermost layer of the multilayer film, thereby lowering contact resistance between the diffusion region and the aluminum alloy film.
Next, a description will be given to the manufacturing method for the conventional capacitance element. FIGS. 10(a) to 10(e) are cross-sectional views illustrating the process of manufacturing the conventional capacitance element.
First, in the step shown in FIG. 10(a), a first platinum film 22a, a ferroelectric film 23a, and a second platinum film 24a are formed sequentially on the substrate 21. Next, in the step shown in FIG. 10(b), the second platinum film 24a is patterned by using a photoresist mask to form the upper electrode 24. Next, in the step shown in FIG. 10(c), the dielectric film 23a is patterned by using a photoresist mask covering a region including the upper electrode 24 to form the capacitance insulating film 23 having the aperture 25. Furthermore, the first platinum film 22a is etched selectively by using a photoresist mask covering the upper electrode 24, the capacitance insulating film 23, and the aperture 25 to form the lower electrode 22.
Next, in the step shown in FIG. 10(d), the interlayer insulating film 26 is formed on the substrate, followed by the first contact hole 27 formed to extend through the interlayer insulating film 26 to reach the lower electrode 22 and the second contact hole 28 formed to extend through the interlayer insulating film 26 to reach the upper electrode 25.
Next, in the step shown in FIG. 10(e), the titanium film and the aluminum alloy film are deposited over the entire surface of the substrate. The titanium film and the aluminum alloy film are then patterned by using a photoresist mask covering the contact holes 27 and 28 and their surroundings to form the first electrode wire 29 to be connected to the lower electrode 22 and the second electrode wire 30 to be connected to the upper electrode 24.
Although each of the first and second electrode wires 29 and 30 is shown as a single-layer film in FIG. 10(e) for the sake of simplicity, it is typically composed of a multilayer film such as the two-layer film consisting of the aluminum alloy film and the titanium film or the three-layer film consisting of the aluminum alloy film, the titanium nitride film, and the titanium film as described above.
In the conventional capacitance element, excellent adhesion is required between the second electrode wire 30 and the upper electrode 24. Moreover, since the capacitance insulating film 23 is typically composed of a ferroelectric material containing a metal oxide as a main component, the platinum film is used to compose each of the upper and lower electrodes 24 and 22 as a material which is unreactive to the metal oxide and capable of withstanding high temperature during thermal treatment. Furthermore, the titanium layer is interposed between the aluminum layer and the platinum layer to compose each of the electrode wires 29 and 30 due to poor adhesion between the aluminum layer and the platinum layer, thereby solidifying the connection between the electrode wires and the electrodes of the capacitance element.
To improve the performance of the capacitance element, thermal treatment is indispensably performed after the formation of the electrode wires 29 and 30 in the manufacturing process. After the heat treatment was performed with respect to the electrode wires 29 and 30, however, the phenomenon was observed in which the performance of the ferroelectric film composing the capacitance insulating film 23 was degraded.
The cause of the degraded performance was tracked down and presumed as follows. The platinum film composing each of the upper and lower electrodes 24 and 22 of the capacitance element has a columnar crystal structure since it is normally formed by sputtering. During the thermal treatment performed with respect to the electrode wires 29 and 30, titanium composing the lower layer of the second electrode wire 30 diffuses into the capacitance insulating film 23 through the grain boundary of the columnar crystal in the platinum film composing the upper electrode 24 to react with the ferroelectric film composing the capacitance insulating film 23, which is the presumed cause of the degraded performance.
The foregoing problem may occur not only in the case where each of the electrodes of the capacitance element is composed of the platinum film but also in the case where it is composed of iridium, palladium, ruthenium, or the like. Even when the lower electrode is composed of a polysilicon film as in a storage node of a memory cell transistor in a DRAM, a similar problem occurs provided that the upper electrode is composed of platinum or the like.
It is therefore an object of the present invention to provide a capacitance element having such a structure that metal composing an electrode is prevented from diffusing into a capacitance insulating film and a manufacturing method therefor, thereby positively preventing the degradation of the properties of the capacitance insulating film, while maintaining excellent adhesion between an upper electrode and an electrode wire.
To attain the object, the present invention has formed an upper electrode having a part kept from contact with a capacitance insulating film such that connection is achieved between the part of the upper electrode and the electrode wire.
A capacitance element according to the present invention comprises: a substrate; a lower electrode composed of a conductor film formed on the substrate; a capacitance insulating film formed on the lower electrode; an upper electrode composed of a metal material and having a first partial film which is in contact with a top surface of the capacitance insulating film and a second partial film which is not in contact with the capacitance insulating film; an interlayer insulating film covering at least the upper electrode; a contact hole extending through the interlayer insulating film and reaching the second partial film of the upper electrode; and an electrode wire filled in at least the contact hole and connected to the upper electrode.
In the arrangement, the second partial film which is not in contact with the capacitance insulating film provides connection between the upper electrode and the electrode wire. This minimizes the possibility that a materiel composing the electrode wire encroaches from the first partial film of the upper electrode into the capacitance insulating film during thermal treatment in the manufacturing process.
In the capacitance element, the second partial film of the upper electrode may have a region in non-overlapping relation with the capacitance insulating film when viewed in plan view and the electrode wire may be connected to the upper electrode at the region of the second partial film in non-overlapping relation with the capacitance insulating film.
The arrangement increases the distance between the second partial film and the capacitance insulating film and more positively prevents the material composing the electrode wire from encroaching from the first partial film of the upper electrode into the capacitance insulating film during thermal treatment in the manufacturing process.
In the capacitance element, the upper electrode may also be formed to be in contact with only a part of the capacitance insulating film, the capacitance element further comprising an underlying insulating film covering at least a part of a region of the capacitance insulating film which is not in contact with the upper electrode, the second partial film of the upper electrode having a region in overlapping relation with the capacitance insulating film when viewed in plan view over the underlying insulating film, the electrode wire being connected to the upper electrode at the region of the second partial film in overlapping relation with the capacitance insulating film when viewed in plan view.
This allows a reduction in the area occupied by the whole capacitance element and further miniaturization of the capacitance element.
In the capacitance element, the capacitance insulating film may also be formed to have substantially the same outer circumferential configuration as the lower electrode, the capacitance element further comprising insulator sidewalls formed on respective side faces of respective outer circumferential portions of the capacitance insulating film and the lower electrode.
In the arrangement, the first and second partial films of the upper electrode are formed continually to present a smoothly curved contour over the capacitance insulating film and the insulator sidewalls in vertical cross section. This suppresses the occurrence of a failure due to discontinuation of the metal film composing the upper electrode at the end portion of the capacitance insulating film.
The capacitance element may further comprise: a capacitance-determining insulating film covering a region of the capacitance insulating film along an outer circumference thereof; and a capacitance determining aperture formed in a region of the capacitance-determining insulating film positioned above a main region of the capacitance insulating film except for the region along the outer circumference thereof, the first partial film of the upper electrode being formed in the capacitance determining aperture.
In the arrangement, the region of the capacitance insulating film in the vicinity of the outer circumference thereof which is susceptible to an influence exerted by peripheral members does not function as a part of the capacitance element, which allows the capacitance element to retain particularly excellent properties and have an accurate capacitance value.
Preferably, a metal material composing the upper electrode includes at least any one of platinum, iridium, palladium, and ruthenium.
Preferably, the upper electrode is composed of at least any two of a platinum film, an iridium film, a palladium film, and a ruthenium film, the two films being stacked in layers.
Preferably, the upper electrode has a columnar crystal structure perpendicular to an underlying surface.
In the arrangement, the metal film composing the upper electrode contains no grain boundary extending in parallel with a film surface thereof, so that a material composing the electrode wire is surely prevented from diffusing from the first partial film into the metal film, reaching the second partial film, and further encroaching in the capacitance insulating film.
Preferably, the capacitance insulating film is composed of any one of a first oxide containing any one of strontium, bismus, and tantalum as a main component, a second oxide containing any one of lead, zircon, and titanium as a main component, and a composite of the first and second oxides.
This suppresses the generation of undesired radiation from an electronic device on which the capacitance element is to be mounted and implements a capacitance element having large capacitance and occupying a minimized area even when it is disposed in a memory cell of a DRAM or non-volatile RAM.
A first method of manufacturing a capacitance element according to the present invention comprises: a first step of sequentially forming a conductor film and a dielectric film on a substrate; a second step of patterning the conductor film and the dielectric film to form a lower electrode and a capacitance insulating film; a third step of forming a metal film for an upper electrode on the substrate; a fourth step of patterning the metal film for an upper electrode to form an upper electrode having a first partial film which is in contact with a top surface of the capacitance insulating film and a second partial film which is not in contact with the capacitance insulating film; a fifth step of forming an interlayer insulating film on the substrate; a sixth step of forming a contact hole extending through the interlayer insulating film and reaching the second partial film of the upper electrode; and a seventh step of depositing a metal film for a wire on the substrate and patterning the metal film for a wire to form an electrode wire filled in the contact hole and connected to the second partial film of the upper electrode.
In the first method of manufacturing a capacitance element, the second step may include etching the conductor film and the dielectric film by using a common mask member to form the lower electrode and the capacitance insulting film having substantially the same outer circumferential configuration as the lower electrode, the method further comprising the step of depositing an insulating film for sidewalls on the substrate and performing anisotropic etching with respect to the insulating film for sidewalls to form insulator sidewalls on respective end faces of respective outer circumferential portions of the capacitance insulating film and the lower electrode, wherein the fourth step may include forming the second partial film of the upper electrode over a region of the substrate including the insulator sidewalls.
A second method of manufacturing a capacitance element according to the present invention comprises: a first step of sequentially forming a conductor film and a dielectric film on a substrate; a second step of patterning the conductor film and the dielectric film to form a lower electrode and a capacitance insulating film; a third step of forming an underlying insulating film on the substrate; a fourth step of partially removing the underlying insulating film to expose a part of the capacitance insulating film; a fifth step of forming a metal film for an upper electrode on the substrate; a sixth step of patterning the metal film for an upper electrode to form an upper electrode having a first partial film which is in contact with a top surface of the exposed region of the capacitance insulating film; a seventh step of forming an interlayer insulating film on the substrate; an eighth step of forming a contact hole extending through the interlayer insulating film and reaching the second partial film of the upper electrode; and a ninth step of depositing a metal film for a wire on the substrate and patterning the metal film for a wire to form an electrode wire filled in the contact hole and connected to the second partial film of the upper electrode.
In the second method of manufacturing a capacitance element, the fourth step may include removing a region of the underlying insulating film positioned above a main region of the capacitance insulating film except for a region of the capacitance insulating film in the vicinity of an outer circumference thereof to form a capacitance determining aperture and the sixth step may include forming the second partial film of the upper electrode in the capacitance determining aperture.
In the second method of manufacturing a capacitance element, the sixth step may include forming the second partial film of the upper electrode on a region of the substrate in non-overlapping relation with the capacitance insulating film.
In the second method of manufacturing a capacitance element, the sixth step may include forming the second partial film of the upper electrode on a region of the underlying insulating film in overlapping relation with the capacitance insulating film.
The first and second methods of manufacturing a capacitance element allows the formation of a capacitance element comprising the capacitance insulating film which is not in contact with the second partial film of the upper electrode which is in contact with the electrode wire. What results is a method of manufacturing a capacitance element having the function of preventing a material composing the metal film for an electrode wire from encroaching into the capacitance insulating film.
In the first and second methods of manufacturing a capacitance element, the step of forming the metal film for an upper electrode is preferably performed by sputtering.
In accordance with the methods, each of the first and second partial films of the upper electrode is formed of the metal film having a columnar structure extending perpendicularly to a film surface. This allows easy formation of the capacitance element wherein the metal film composing the upper electrode contains no grain boundary extending in parallel with a film surface thereof and a material composing the metal film for an electrode wire is surely prevented from encroaching into the capacitance insulating film.